1. Technical Field
The present invention relates to nuclear a reactor vibration monitoring apparatus and a method of monitoring nuclear reactor vibration, which monitor vibrational state of reactor internal including the jet pump installed in a reactor pressure vessel of a nuclear reactor.
2. Background Art
By referring to the case of a general boiling water reactor (BWR) as an example, an internal structure of a reactor pressure vessel (hereinafter, referred to as a RPV) and the jet pump will be explained. The boiling water reactor (BWR) has a RPV, as described in Japanese Patent No. 3782559. The RPV generally has an almost cylindrical shape, and one end thereof is closed by a bottom head, and the other end thereof is closed by a removable upper head. The jet pump is installed inside the RPV.
Due to the installation of the jet pump, cooling water more in volume than the amount of cooling water sucked outside the RPV can be supplied to a core by a recirculation pump.
The jet pump has a nozzle, a throat, and a diffuser. The throat and diffuser are connected to each other by a slip joint. A gap is formed between the throat and the diffuser. The nozzle is disposed above the throat. Driving water which is cooling water is jetted from the nozzle inward the throat. When there exists a pressure difference between outside and inside the slip joint, a part of cooling water flowing from the throat into the diffuser flows out from the jet jump through the gap.
As mentioned above, the jet pump generates an internal high-speed flow, a mixed flow, and a leakage flow from the gap of the slip joint, so that it is an apparatus affected by a flow-induced vibration. The vibrational state of the jet pump must be monitored and evaluated to ensure long-period soundness of the jet pump. The jet pump is an example of an apparatuses to be evaluated like this.
The method of monitoring vibration and vibration monitoring apparatus are, for example, described in Japanese Patent No. 3782559, and Japanese Patent No. 4551920. For example, Japanese Patent No. 3782559 describes the nuclear reactor vibration monitoring apparatus. In the nuclear reactor vibration monitoring apparatus, ultrasonic waves are transmitted from an ultrasonic sensor installed on an outside surface of the RPV to the jet pump via the RPV and reactor water in the RPV and the change of propagation time of the ultrasonic waves is measured based on ultrasonic velocity of the RPV, ultrasonic velocity of the reactor water, thickness of the RPV, and a distance between the RPV and a reactor internal in the RPV, thus the vibration amplitude of the reactor internal is obtained.
Further, in a vibration and degradation monitoring apparatus described in Japanese Patent No. 4551920, a corner reflector including a plane-shaped reflection surface capable of reflecting ultrasonic waves and an orthogonal plane as a reflection surface is attached to the surface of a monitoring object. The apparatus receives the ultrasonic waves reflected on the reflection surface of the reflection body and measures a vibration displacement of the monitoring object based on the received ultrasonic waves.
Furthermore, Japanese Patent Laid-Open No. 2011-133241 discloses a nuclear reactor vibration monitoring apparatus which can detect vibration of a reactor internal which is sloped and curved without attaching a reflection plate, by identifying and removing reflected ultrasonic pulses reflected from a wall inside of the RPV.